BAGHDAD, Iraq – An American helicopter crashed in a desert sandstorm in the early morning darkness yesterday, killing the 30 Marines and one Navy sailor aboard. Six other troops died in insurgent ambushes in the deadliest day for Americans since the Iraq war began nearly two years ago.

Only days before Iraq’s crucial elections Sunday, insurgents set off at least eight car bombings that killed 13 people and injured 40 others, including 11 Americans. The guerrillas also carried out a string of attacks nationwide against schools that will serve as polling centers.

In Washington, President Bush called on Iraqis to defy terrorism and go to the polls despite relentless insurgent attacks.

The CH-53E Super Stallion was carrying personnel from the 1st Marine Division on a security mission in support of the election when it went down about 1:20 a.m. near the town of Rutbah, about 220 miles west of Baghdad, the military said.

The crash occurred during severe weather, but its cause was still under investigation, said the chief of American Central Command, General John Abizaid. An Accuweather map showed sandstorms yesterday in the western region of Iraq near the Jordanian border where the crash took place.

A search and rescue team was at the site. The 30 Marines and one sailor killed were the most American service members to die in a single incident since the March 2003 invasion of Iraq, Lieutenant General John Sattler, the top Marine commander in Iraq, said.

The deadliest previous incident for American troops was also a helicopter crash: a November 2003 collision of two Black Hawk helicopters that killed 17. Before yesterday’s bloodshed, the most Americans killed in one day came on the invasion’s third day – March 23, 2003 – when 28 troops were killed during the American military’s drive to take Baghdad and topple Saddam Hussein.

The American military has not seen such a high loss of life in one day in 15 years – since an explosion ripped through a gun turret on the USS Iowa during a training exercise in the Caribbean in April 1989, killing 47 sailors.

All but three of the Marines killed yesterday had been based in Hawaii, according to Senator Akaka, a Democrat of Hawaii.

Iraqi security forces and civilians have borne the brunt of violence in Iraq, with bombings often killing scores of people at a time. More than 180 people were killed on March 2, 2004, during a string of suicide attacks at Shiite shrines in Karbala and Baghdad.

Violence has only increased ahead of Sunday’s election, which will create a 275-member National Assembly and regional legislatures. Sunni Muslim extremists have threatened to sabotage the election, and many Sunni clerics have called for a boycott because of the presence of American and other foreign troops.

The group calling itself Al Qaeda in Iraq warned people to stay away from the polls, threatening attacks. “Oh people, be careful. Be careful not to be near the centers of infidelity and vice, the polling centers. … Don’t blame us but blame yourselves” if harmed, a Web statement issued in the group’s name said.

In addition to yesterday’s crash deaths, four Marines were killed in fighting in Iraq’s Anbar province, the military said.

A reporter embedded with those troops, Jim Dolan of WABC in New York City, said the deaths came when insurgents ambushed a Marine convoy leaving the town of Haditha, northwest of Baghdad, hitting a vehicle with a rocket-propelled grenade.

Also yesterday, insurgents attacked an American Army patrol near the northern town of Duluiyah, killing one soldier and wounding two others, and in the Baghdad area a roadside bomb killed another soldier and wounded two others, the American command said.

Political violence continued. Several schools slated to be used as polling stations were bombed overnight.

A suicide bomber detonated a fuel tanker at the offices of the Kurdistan Democratic Party in the town of Sinjar, southwest of Mosul, killing five and injuring at least 20 people, KDP officials said.

Earlier in the day, gunmen opened fire with machine guns on the local headquarters of the Patriotic Union of Kurdistan and the Communist Party in the city of Baqouba, north of Baghdad, killing a traffic policeman. The KDP and PUK are the two largest Kurdish groups in Iraq and have formed a coalition with other Kurdish groups to run in the election.

Insurgents also set off three car bombs in rapid succession in the town of Riyadh, north of Baghdad, killing at least five people – including three policemen.

Four American soldiers were injured in a car bombing yesterday in Saddam’s hometown of Tikrit, the American command said. Another car bomb targeted a multinational forces convoy on the road to Baghdad’s international airport, injuring four soldiers, the command said.

The attack temporarily closed the airport road, one of the country’s most dangerous.

Another car bombing later hit the same airport road, and an eighth car bomb detonated prematurely in the town of Mashahda, 30 miles north of Baghdad, killing the two men in the car.

Also yesterday, on pan-Arab TV, Mr. Bush said that Iran should stay out of Iraq’s elections.

“Iranians should not be trying to unduly influence the elections,” Mr. Bush said of Sunday’s polls in an interview with the Dubai-based satellite channel Al-Arabiya, according to a White House transcript.

American and Iraqi officials have expressed fears that Iran, a Shiite Muslim-majority state on Iraq’s eastern border, is trying to expand its influence through the elections, in which Iraqi Shiites are expected to win the largest number of seats in a transitional national assembly.

Iran has rejected accusations it was trying to influence the elections, saying that Iraqis have made it clear they won’t take orders from abroad.

Mr. Bush said he does not think the elections will produce a pro-Iranian government in Baghdad.

“The future of Iraq depends upon Iraqi nationalism and the Iraq character – the character of Iraq and Iraqi people emerging. You know, there’s been longtime problems between Iran and Iraq, and I’m confident that Iraqi nationalism and Iraqi pride and the history of Iraq and traditions of Iraq will be the main focus of the new government, and reflect the new government,” he said.

Mr. Bush also paid tribute to Iraqis and urged them to vote this weekend.

“I know thousands and thousands of Iraqis want to vote. I know they cherish the idea of being able to vote, and I hope as many Iraqis vote as possible,” he said.

He said the elections presented Iraqis with a “historic opportunity.”

“I’m proud of the country. I’m proud of the citizens, and look forward to the day when Iraq is democratic and free, with Iraqi traditions and Iraqi customs.”

He also singled out Iraq’s minority Sunni Muslim community. “I hope all the Sunnis vote,” Mr. Bush added.

Sunni leaders have called for a boycott of the polls, arguing they cannot be free and fair due to persistent violence in Iraq and the American military presence.

The Sunni minority wielded great influence under Saddam. Many insurgents are Sunnis.

Views among Iraqi Shiites toward Iran range from hate to devotion. Despite 60% of Iraq’s 26 million people being Shiite, many harbor resentment toward Iran over the bloody 1980-88 war between the countries in which 1 million people died. Many Iraqis also accuse Iran of sponsoring this country’s rampant insurgency.

But many Iraqi Shiites, who were suppressed under Saddam’s three decade rule, also look to Iran’s Shiite establishment for religious guidance.

Mr. Bush expressed sorrow for the loss of life in yesterday’s deadly helicopter crash.

“Today a tragic helicopter accident is a reminder of the risks inherent in military operations,” the president said. “But I am convinced we’re doing the right thing by helping Iraq become a free country, because a free Iraq will have long-term effects in the world.”